The field of the present invention relates to handling of metal-working fluid. In particular, methods and apparatus are described herein for treating metal-working fluid for re-use.
Currently-used aqueous metal-working fluid formulations contain agents such as biocides, extreme pressure additives, antioxidants, corrosion inhibitors, dyes, water conditioners, and so forth. These agents may comprise formaldehyde, ethanolamines, chlorinated compounds, detergents, nitrites, nitrates, phosphates, borates, and other organic and/or inorganic compounds. Furthermore, aqueous metal-working fluids are prone to microbial contamination and for this reason often contain biocides. Recognized diseases associated with metal-working fluid include contact dermatitis, work-related asthma, and hypersensitivity pneumonitis. It is evident that many metal-working fluid agents as well as microbial contaminants are harmful to metal workers and the environment.
Long term debilitating conditions due to contact with contaminated metal-working fluid and increased burden on the environment demand effective management methods. However, management of metal-working fluid is technically difficult and expensive. Machining operations employ elaborate enclosures to control the dispersal of metal-working fluid mists. Contaminated metal-working fluid must be evaporated and/or transported to dump sites by certified agents. Management of contaminated metal-working fluid by disposal results in its accumulation in landfills and dump sites. More importantly, worker health issues cannot be ignored. There are over two million metal workers in the United States alone, and the industry is growing and with that growth arises the potential to expose even more workers to metal-working fluid exposure hazards.
Tool grinders and saw fillers using carbide or stellite tipped tools may develop asthma or hard metal lung disease. These health-debilitating conditions are currently viewed as a result of exposure to cobalt, although other transition and/or heavy metals may also be implicated. Two principal features of hard metal lung disease are inflamed and scarred alveolar tissue. Treatment of these conditions includes medication and perhaps removal from the work place. However, not all patients may respond to treatment. There are other diseases reported to be associated with cobalt exposure. Some of the reported diseases are contact dermnatitis, eczema, cardiomyopathy and lung cancer. Whether these medical conditions arise through exposure to metal particulates or exposure to aqueous solutions containing metal ions (liquid or mist) has not been elucidated.
Biocides have been used for years in an attempt to control microbial contamination in metal-working fluid as well as other fluids. The addition of such biocides represents an added expense, and is also difficult to control. Some studies show that they are effective for only a brief period of time and never completely inhibit bacteria and other microbes. Furthermore, biocides may induce selection in mycobacteria, recently associated with hypersensitivity pneumonitis, and other microbes, thereby producing resistant strains of these micro-organisms. Byproducts of microbial contamination may also pose health risks to and/or create an unpleasant work environment for metal workers. In particular, significant microbial contamination is often also accompanied by production of hydrogen sulfide, a malodorous and potentially harmful contaminant.
The Safe Drinking Water Act requires disinfection of all public water supplies. It further requires the Environmental Protection Agency (EPA) to set standards and establish processes for the treatment and distribution of disinfected water. The Act ensures that no significant risks to human health arise from public water supplies. Disinfectants and filtration systems are currently acceptable methods for treating water supplies. However, EPA has evidence linking disinfectant byproducts to cancers and other toxic effects.
EPA actively seeks innovative technology to upgrade existing methods. These new technologies may include alternatives to chlorine, innovative applications of V irradiation, and other processes that improve methods of treating public water supplies. The agency""s goals are to develop new methods that remove organic and inorganic compounds as well as particulate matter and pathogens. The organic and inorganic compounds of particular interest may include perchlorates, aluminum, pesticides, arsenic, nitrates, and radium. Pathogens of particular interest may include cryptosporidium, caliciviruses, microsporidia, echoviruses, and adenoviruses.
It is therefore desirable to provide apparatus and methods for treating metal-working fluid that addresses the problems associated with contaminated metal-working fluid, exposure thereto, and disposal thereof.
Certain aspects of the present invention may overcome one or more aforementioned drawbacks of the previous art and/or advance the state-of-the-art of treatment of metal-working fluid, and in addition may meet one or more of the following objects:
To provide apparatus and methods for treating metal-working fluid whereby the useful life of the metal-working fluid is extended;
To provide apparatus and methods for treating metal-working fluid wherein the likelihood of metal-working fluid exposure-related illness in metal workers is reduced;
To provide apparatus and methods for treating metal-working fluid wherein particulates are filtered from the metal-working fluid;
To provide apparatus and methods for treating metal-working fluid wherein microbial contamination may be suppressed and/or eliminated without using biocides;
To provide apparatus and methods for treating metal-working fluid wherein microbial contamination may be suppressed and/or eliminated by heating the metal-working fluid;
To provide apparatus and methods for treating metal-working fluid wherein the metal-working fluid is agitated and/or aerated during treatment;
To provide apparatus and methods for treating metal-working fluid wherein gaseous and/or malodorous contaminants are removed by aeration and/or filtration;
To provide apparatus and methods for treating metal-working fluid wherein concentrations of cobalt and/or other metal ions are reduced by treatment of the metal-working fluid;
To provide apparatus and methods for treating metal-working fluid wherein concentrations of cobalt and/or other metal ions are reduced by passing the metal-working fluid through an ion-exchange medium;
To provide apparatus and methods for treating metal-working fluid wherein metal-working machine down time due to metal-working fluid treatment is reduced or substantially eliminated; and
To provide apparatus and methods for treating metal-working fluid that may be readily and/or economically implemented in a typical metal-working work environment.
One or more of the foregoing objects may be achieved in the present invention by a method for treating metal-working fluid comprising the steps of: a) transferring the metal-working fluid into a heating vessel; b) heating the metal-working fluid in the heating vessel to maintain the metal-working fluid at an elevated temperature during a heating period; c) agitating and aerating the metal-working fluid during the heating period; d) transferring the metal-working fluid out of the heating vessel into a holding vessel after the heating period; and e) transferring the metal-working fluid out of the holding vessel. The fluid may pass through a particle filter before entering the heating vessel, and it may be heated to between about 145xc2x0 F. and about 210xc2x0 F. for at least about 30 minutes while in the heating vessel. During heating, heated ambient air may be drawn through air inlets and through the metal-working fluid to agitate and aerate the metal-working fluid, thereby ensuring substantially uniform heating and extracting gaseous contaminants. Mist and gaseous contaminants are substantially removed from the airflow prior to its release into the surroundings. After the heating period the treated metal-working fluid is transferred into a holding vessel and ultimately back to a metal-working machine for re-use. The metal-working fluid may flow through an ion-exchange medium to reduce concentrations of cobalt and/or other metal ions before transfer of the fluid back to a metal-working machine.
One or more of the foregoing objects may be achieved in the present invention by an apparatus for treating metal-working fluid, the apparatus comprising: a) a heating vessel; b) a heater for heating the metal-working fluid in the heating vessel to an elevated temperature to maintain the metal-working fluid at the elevated temperature during a heating period; c) an agitator for agitating the metal-working fluid during the heating period; d) an aerator for aerating the metal-working fluid during the heating period; e) a holding vessel; and f) a pump for transferring the metal-working fluid from the heating vessel into the holding vessel after the heating period. The apparatus may further include a particulate filter through which the metal-working fluid may flow before and/or during transfer into the heating vessel, and an ion exchange medium through which the metal-working fluid may flow before and/or during transfer back to a metal-working machine.